1. Field of the Invention
The present invention relates to a solid-state imaging device, a method of manufacturing a solid-state imaging device, and an electronic apparatus. In particular, the invention relates to a solid-state imaging device, a method of manufacturing the solid-state imaging device, and an electronic apparatus using the solid-state imaging device by which images with high quality can be obtained.
2. Description of the Related Art
Solid-state imaging devices have been incorporated in various electronic apparatuses, for example, imaging apparatuses such as digital still cameras, video cameras, etc. and mobile terminal apparatuses having an imaging function, for a variety of uses. The solid-state imaging devices include APS (active pixel sensor) having amplifying elements on a pixel basis, and CMOS (complementary MOS) image sensors in which signal charges accumulated in photodiodes provided as photoelectric conversion elements are read out through MOS (metal oxide semiconductor) transistors are in wide use.
A unit pixel in a CMOS image sensor according to the related art has, for example, a photodiode having an HAD (Hole Accumulated Diode) structure and an FD (Floating Diffusion) region disposed on the opposite sides of the photodiode with respect to a transfer gate. In addition to these components, the unit pixel has a reset transistor, a selecting transistor, and an amplifying transistor.
In a CMOS image sensor, in general, a readout operation of reading out the signal charge accumulated in each photodiode is carried out on the basis of each row in a pixel array, and the pixels for which the readout operation is finished restart accumulation of electric charge at the moment the readout operation is finished. Since the readout operation is thus performed on the basis of each line in the pixel array, in the CMOS image sensor, the signal charge accumulation periods cannot be made coincident for all the pixels. In the case where the subject to be imaged is moving or in other similar situations, therefore, the image obtained would be distorted. For instance, when a subject which is straight shaped in the vertical direction and which is moving horizontally is shot, the subject is imaged as if it were inclined.
In order to obviate the generation of such a distortion of image, there has been developed an all-pixel-simultaneous electronic shutter for CMOS image sensor such as to realize the same exposure period for all the pixels. The all-pixel-simultaneous electronic shutter is a shutter ensuring that exposure is started simultaneously and finished simultaneously for all the pixels effective for imaging, and such a system is also called global shutter (global exposure).
As a method for realizing the global shutter in a CMOS image sensor, for example, there is a method in which an electric-charge holding region is provided between the photodiode and the FD region in each pixel. Where each pixel is provided with the electric-charge holding region, the area of the photodiode is restricted, whereby the saturated electric-charge amount is reduced, as compared with that in a pixel structured without the electric-charge holding region.
In view of the foregoing, the present applicant has proposed a pixel structure in which a photodiode and a electric-charge holding region are integrally united together through an overflow path, in order to obviate a reduction in the maximum electric charge amount of a photodiode (see, for example, Japanese Patent Laid-open No. 2009-268083, hereinafter referred to as Patent Document 1).